1. Field of the Invention
The present invention relates to a method of evaluating semiconductor devices, a method of designing semiconductor devices and a method of producing the semiconductor devices. More specifically, the invention relates to a method of evaluation for producing semiconductor devices made up of the transistors that exhibit highly reliable characteristics and a method of producing semiconductor devices.
2. Description of the Related Art
Among transistors, a MOS transistor using a gate oxide film has heretofore been widely used. Accompanying the demand for fabricating MOS transistors in reduced sizes yet having improved performance, is a demand to form the gate oxide film with a reduced area and a reduced thickness.
The gate oxide film, however, often undergoes insulation breakdown due to defects in the steps of production, erroneously designing or conditions in which it is used, and it is becoming important to enhance the reliability of the gate oxide film, the properties of the gate oxide film and the life thereof.
In order to improve the reliability of transistor characteristics, therefore, it is necessary to properly evaluate the performance and properties of the gate oxide film.
It is further becoming necessary to investigate the reliability of the gate oxide film of the transistor by evaluating TDDB (time dependent dielectric breakdown) characteristics or QBD (Q-breakdown) characteristics, as an example, to evaluate the quality and characteristics of the semiconductor device for each generation of technology or for each processing technology.
So far, however, the reliability of the gate oxide film has been investigated and evaluated by practically forming an oxide film on a MOS capacitor or the like, relying upon the processing technology that is to be used, and conducting the testing.
Accordingly, problems occur as described below.
(1) An element is formed on which an oxide film is practically formed and the testing is, then, carried out. An extended period of time is required before the test results are obtained.
(2) The testing pattern is made up of an ordinary MOS capacitor which, however, is different in shape from the gate oxide film of the MOSFET. It is not therefore possible to use the data obtained from the MOS capacitor as data for the gate oxide film.
(3) Even when a MOSFET testing pattern is formed as the gate oxide film, a new pattern for evaluation must be formed for every progression of the generation in the LSI.
(4) Reliability of the gate oxide film is affected depending upon its shape, but it is difficult to verify the effects of the shapes in a distinct manner.
So far, therefore, a considerable period of time was required for evaluating the reliability of the gate oxide film that is a basis for evaluating the characteristics of the semiconductor device, i.e., for evaluating characteristics, performance, shape, etc. of the transistor. Besides, it is difficult to evaluate the desired gate oxide film from the obtained data. Moreover, even when the gate oxide film was evaluated, the data were not adapted to evaluating the gate having a different form. Therefore, the evaluation operation had to be repeated for each of the steps for producing transistors and each of the production conditions.